1. Field of the Invention
The invention relates to a heat sensor system, and particularly to an alarm trigger and a heat sensor used as a triggering device in a fire alarm.
Residential and industrial fire detection systems may be broadly categorized as smoke alarms and heat-sensor triggered alarms. The most recent figures available from the U.S. Fire Administration reveal that 6,000 lives were lost in a one-year span, and over $8 Billion of direct financial losses were sustained in the U.S. due to fires. While no national standard has been reached, a voluntary standard suggests heat sensors throughout the house and a smoke detector centrally disposed. There are mandatory as well as voluntary requirements. Costs for such a systems range from $10 for a single smoke alarm to well over $1,000 for a system with several smoke alarms and heat sensors.
The correct placement and use of fire alarms is considered by fire fighting authorities as one of the principal methods of fire control. Approximately 85% of homes, and virtually all commercial and industrial buildings in the U.S. are equipped with fire alarms of one type or another. The objective of the fire alarm is to emit a signal which alerts occupants to seek exits, activates fire suppression systems or otherwise notifies fire control personnel.
2. Description of the Related Art
There are several systems for classifying the stages of fire. One of the classification systems includes the following stages:
HEATING
DECOMPOSITION
IGNITION
COMBUSTION AND PYROLYSIS
PROPAGATION (FLAME SPREAD)
PENETRATION
"FLASHOVER" ( FULGURATION )
INCINERATION
Most prior art fire detection systems do not respond to the first three stages, and are activated only starting with the fourth stage (combustion and pyrolysis). Infrared detectors could pick up initial heating, if set for automatic detection. Such systems, however, are not widely used as they are expensive, difficult to install, operate and maintain, and they require proper strategic placement.
Several types of detectors are commonly in use: thermal sensors (thermostats, thermopiles and infrared sensors); smoke detectors (photo-electric and ionization detectors); and flame detectors; and product of combustion (gas) detectors. Each type has major drawbacks. Most depend on "line-of-sight", or proximity, for their efficiency, and are frequently blocked from "direct view" of the source locus of the fire.
In many fire alarm systems the sensor component of the system is attached directly to the alarm circuit. The fire signal is picked up from a distance, after a trajectory through intervening space. The sensitivity and thus the effectiveness of the alarm is thus strongly affected.
Since the objective of the alarm component is to alert inhabitants to impending danger, there are numerous types of system outputs to serve this function: sirens, bells, horns, buzzers, loudspeakers, flashing lights, telecommunication signals, etc.
Heat sensors, on the other hand, are based on fire detection by fusible links or other mechanical devices, such as bi-metal trigger probes. The response speed and sensitivity of these devices are essential engineering problems. Since heat sensors must be disposed at least one per room in order to be effective, the cost of installation therefor is quite substantial. In many instances, these devices must be replaced once they have been triggered, adding to the cost of maintenance.
One of the most popular smoke alarm devices is available under the trademark FIRST ALERT, as sold by PITTWAY Corp. Pitway says smoke detectors in general should not be placed in areas with a relatively high density of combustion particles, such as in kitchens, garages, near furnaces, hot water heaters and space heaters. Furthermore, such devices may be triggered by dust, which prevents their use in many industrial environments. Numerous other "forbidden" areas are listed for ionization or smoke detectors, such as in damp or very humid areas, very cold or very hot rooms, bathrooms, dirty areas, near air vents, insect-infested areas and near fluorescent lights.